Practical Ways to Select the Proper Motorcycle Fork Length

//Practical Ways to Select the Proper Motorcycle Fork Length

Practical Ways to Select the Proper Motorcycle Fork Length

Today’s post will help you guys who are taking on a new bike build. As a tech here at J&P Cycles, I’m often asked how long a fork I should purchase? There’s really no way for me to answer that question because it’s something you must decide for yourself. That being said, here’s an explanation of the easiest way I have found to help people arrive at the best answer. 

  • First, we need to mock up the rear wheel we’re going to use with the frame we have.
  • Next — and most important — we’re going to block the front of our chassis up to give us the ride height and “look” that we want. Once this is established, everything else is downhill.
  • We also need to know the radius of the wheel/tire combination we are going to run. For a 16-inch or a 21–inch, we’ll use a radius of 13 inches. For a 19–inch, we’ll use a radius of 12 inches
  • Take a broomstick or mop handle and drop it through the steering neck. Of course, now you’ll need to know use what wheel radius we are running up front in order to get our first dimension point.
  • Measure the radius of the wheel we’re going to use from the broomstick (straight to the floor), and then mark the broomstick at that point. (this mark represents our axle center).
  • Next, measure from the point of the mark to the top of the frame. This gives us the desired fork length.

A stock FXST has a fork length that is very close to 32 inches. If you need a 34-inch length fork, you would need to order a +2 fork. If you need 38-inch fork, then +6 is what you’ll need. If you need a fork shorter than 32 inches, we would select -2 or -4 (depending on what you measure).

OK, we’ve talked about tube type forks, but Springer’s measure slightly differently. According to Paughco, the builder of the highest-quality, largest-volume custom Springer’s available today, the measurement is also from the top tree (top of the steering neck), but the bottom measurement goes to the center of the rear leg pivot. For a Springer, the stock length is considered to be 27 inches. A stock HD late-model Springer is +3 inches (30 inches) for comparison purposes.

As always, our dedicated tech staff is available to answer any of your questions. Reach them via e-mail, phone or chat (to get started, visit the J&P Cycles Customer Service page today).

By |2014-03-28T16:27:54+00:00June 14th, 2010|Categories: Tech Tips|Tags: , , , |17 Comments

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  1. tom moore May 9, 2016 at 4:00 pm

    I have an 84 Honda shadow vt700, its rare I find any after market parts, im buying a springer front end and will tweek where needed, these bikes came with a 32 degree rake, I cant find a raked triple tree for it because I want to chop it, so my question is if I buy these springers and they are to long wich I have the feeling tbey are can I # 1 weld a piece on the bottom neck redrill it to catch some rake with the neck bolt or can I cut them to shorten them

  2. CLAY Laird March 21, 2016 at 4:31 pm

    Interested in pitting springer front end on 2013 softball deluxe. Suggestions? 5ft 6 ” running ::) Nguyen jockey shift.

  3. Sean October 3, 2015 at 6:51 pm

    Sorry to chuck a spanner in the works but don’t you have to take tree offset and fork compression into account? Otherwise you’d end up with forks too short and your ride height will drop lower. I thought you add tree offset AND 1-1.5″ (depending on spring rate) for compression. For example, if broom handle measurement is say 27″, tree offset is 2.5″ and allow 1.25″ for compression you actually would need a total overall length of 30.75″ to arrive at your required ride height.

  4. March 4, 2015 at 4:30 am

    Really no matter if someone doesn’t understand after that its up to
    other people that they will help, so here it happens.

  5. chester magoun January 24, 2015 at 10:43 pm

    I building a trike using a 1972 Toyota carina 4cyl. Engine auto.and rear end.coil over rear susp.i want to put a harley front end with 12in. Longer legs at a 38 degree rake.or a 12 over springer with a 42 degree rake .can you help me with these using a 21in.wheel

  6. Anthony Pettrey June 30, 2014 at 7:03 pm

    btw, if it helps, my tire it runs on the front is a 2.25/17

  7. Anthony Pettrey June 30, 2014 at 6:59 pm

    Hello all. I have a strange project and need some help. before i get into the guts of the question i just want to ask that no one give me crap due to the bike choice, im poor and work with what i can afford.
    I have a Pagsta mini, looks like a Honda Rebel knockoff. It has the tube style forks and i am wanting to switch those out for springers. I also am pondering angled tripple trees. Ultimately my goal is to lengthen the bike and raise height so ultimately i will also be welding a ridgid end onto it instead of the swaybar rearend and putting on dif size wheels. I measured the forks in two places. 21 inches or so from the cross member at the neck base (not sure of correct term) , 27 or 28 from the triple tree. Soooo to find a classic chopper style springer that would be applicable what should i do?? Please forgive my ignorance but i do think once completed this should be quite a conversation worthy bike.
    Thanks for any and all help

  8. Lilricky January 22, 2014 at 11:12 am

    I am wanting to change from a glide front end to a springer front end. I am wanting to check the trail to make sure I dont need to do any other changes to the frame rake to get proper tail. i need to know how to measure trail on a springer front end. any help with this would be helpfull. All of the rake trail calculaters i have found tell how to measure trail with a glide, but say nothing on springers.
    Thank You for any help,
    Lil Ricky

  9. Lance Dickwood July 1, 2010 at 9:43 am

    Back in the day, before we ever heard of rake & trail, I’d remove the front end, make a chalk line on the garage floor, cut the gusset side of the neck with a torch, stick an iron pipe through the neck, heat the neck, and bend it up with the pipe until I thought it looked right.

    I guess math is cool, but “looks right” is “right” always works better . . .

    • Rob January 6, 2015 at 9:15 am

      Seriously, your name is dickwood?

  10. […] like to understand how to select the proper length fork tubes, feel free to read our blog post on Practical Ways to Select the Proper Motorcycle Fork Length from senior J&P technician Scott […]

  11. matt96fxstc June 19, 2010 at 2:03 pm

    I’d like to see something on how to plan fork length and trees when changing the rake angle to maintain the same ride height, or is this just something that needs to be figured out using the process described in the article?

  12. matt96fxstc June 19, 2010 at 2:01 pm

    Id like to see something about changing rake angle with trees and how to figure out fork length to maintain the same ride height, or is this something that just needs to be figured out using the process described in the article?

  13. matt96fxstc June 19, 2010 at 1:58 pm

    I’d like to see something about rake and fork to figure what fork length to porder when changing the rake of the trees to maintain the same ride height. Or is this just something that need to be figured out by using the process mentioned in the article??

  14. Monica S. June 17, 2010 at 8:10 am

    Hi, I’m very interested in Linux but Im a Super Newbie and I’m having trouble deciding on the right distribution for me (Havent you heard this a million times?) anyway here is my problem, I need a distribution that can switch between reading and writing in English and Japanese (Japanese Language Support) with out restarting the operating system.

  15. Ben June 15, 2010 at 8:24 am

    Good article but I think it would be more helpful if you would use actual pictures of the bulleted process. Visualization helps out a lot for things like this.

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